This invention relates to a liquid dispensing and vapor recovery system and, more particularly, to such a system in which liquid is dispensed from a storage tank to a receptacle while vapors from the receptacle are passed to the storage tank.
With the increased emphasis on preventing pollution of the atmosphere, recent attention has been directed to minimizing the introduction of gasoline vapors into the atmosphere from both permanent type underground storage tanks for the gasoline, and from the vehicles into which the gasoline is dispensed.
Gasoline vapors can easily be recovered from underground storage tanks by providing a separate vapor return line which connects the storage tank to the transport truck which periodically fills the tank. In this manner, the gasoline introduced into the tank from the transport truck will displace the vapors and force them through the vapor recovery line to the truck whereby they are ultimately disposed of either by burning or through compression-refrigeration systems.
In each of U.S. Pat. Nos. 3,905,405; 3,915,206; 3,913,633; 3,941,468; 3,952,781; 3,981,334 and 3,981,335, all of which are assigned to the same assignee of the present invention, a gasoline dispensing and vapor recovery system is disclosed which enables a very high percentage of vapor recovery from automobile fuel tanks to be achieved. In these arrangements an eductor (also termed an "injector" or "aspirator") is provided which establishes a reduced pressure zone in response to fluid flow from the storage tank to the vehicle tank, with the reduced pressure zone functioning to draw the vapors from the receptacle back to the tank.
Since these arrangements are designed for installations in which the storage tank can be located a distance below the dispensers so as to accommodate the proper (approximately 1/8 inch per foot) slope therebetween to enable the gasoline utilized in the aspirator to flow by gravity back to the storage tank, problems are created when, due to limitations in the terrain and other related factors, such a slope cannot be maintained. In large installations, where many dispensers are utilized and where there may be as much as 200 feet between the tank and some of the dispensers, this problem is especially acute. In addition, when all of the dispensers of a multi-dispenser installation are operating at the same time, it is difficult for a single standard return line to accommodate the high volume of vapor and gasoline passing through the aspirator.